A known example of conventional mounting techniques for large-scale integration (LSI) is one that uses through silicon via (TSV) technology. Silicon substrates having through silicon vias are widely used, for example, as interposers. An interposer is a substrate that interconnects a pair of circuit boards differing in routing design rule and in terminal pitch such as a pair of an integrated circuit (IC) and a printed board.
There is known a method for forming TSVs in a silicon substrate, in which, as described in Non Patent Literature 1, TSVs are formed before, after, or between the steps of forming elements such as a transistor or forming a circuit including electrodes.
The TSV technology unfortunately requires high cost because this technology uses a silicon substrate, which is expensive, and because it involves, due to the use of silicon which is a semiconductor, an insulation treatment performed before and after the formation of through holes in the silicon substrate. In terms of, for example, cost reduction of interposers, attention has been given to glass substrates with through glass vias (TGVs) which are produced by forming through glass vias in a glass substrate which is inexpensive.
The TGV technology involves the formation of through holes in a glass substrate. A known example of the technique for forming through holes in a glass substrate is one in which, as described in Patent Literature 1, the formation of through holes is accomplished by irradiation with a pulsed YAG laser. Additionally, Patent Literature 2 describes a method for forming minute holes in a photosensitive glass substrate. In the method described in Patent Literature 2, a photomask is placed on a predefined region of the photosensitive glass substrate, and the photosensitive glass substrate is irradiated with ultraviolet light to form a latent image. The photosensitive glass substrate is then heated to crystallize the latent image. Next, a processing target hole smaller than the latent image is formed by laser light at the center of the area where the latent image lies. This is followed by etching using hydrofluoric acid. The crystallized area is thus selectively etched, with the result that a hole is formed. Patent Literature 3 describes a method for perforating a glass sheet from both sides of the glass sheet using a pair of upper and lower coaxial core drills opposed across the glass sheet.